Apparatus and method for transmitting and receiving sounding signal in a wireless communication system

ABSTRACT

In a wireless communication system, at least one sounding subchannel determining parameter is transmitted from a sounding signal receiving apparatus to a sounding signal transmitting apparatus. A sounding subchannel for the sounding signal transmitting apparatus is allocated according to the sounding subchannel determining parameter. A sounding signal is received from the sounding signal transmitting apparatus over the allocated sounding subchannel. The sounding subchannel determining parameter is determined for allocating a sounding subchannel considering a frequency correlation.

CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY

The present application is related to and claims the benefit under 35U.S.C. §119(a) of a Korean Patent Application filed in the KoreanIntellectual Property Office on Feb. 5, 2010 and assigned Serial No.10-2010-0011210, the entire disclosure of which is hereby incorporatedby reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to an apparatus and method fortransmitting and receiving a sounding signal in a wireless communicationsystem.

BACKGROUND OF THE INVENTION

A wireless communication system generally uses a multi-sector approach,and performance of a Mobile Station (MS) located in a sector boundaryregion significantly deteriorates due to Inter-Sector Interference(ISI). Therefore, it is necessary to reduce ISI in order to improve theoverall system performance of the wireless communication system.

Meanwhile, if it is possible to detect channel information of MSs, aBase Station (BS) can significantly reduce ISI by using multi-sectorcooperative beam forming. Therefore, various schemes for detectingchannel information of MSs have been proposed, such as a scheme ofdetecting channel information using a sounding signal. The scheme ofdetecting channel information of MSs using the sounding signal isdescribed below.

In a wireless communication system using Time Division Duplex (TDD)Orthogonal Frequency Division Multiplexing (OFDM), because an uplink anda downlink are identical to each other in channel characteristics, whenan MS transmits a sounding signal to a BS over the uplink, the BS maydetect channel information of the MS using the sounding signal. Forconvenience of description, the wireless communication system using TDDOFDM will be referred to as a TDD OFDM wireless communication system,and one example of the TDD OFDM wireless communication system is anInstitute of Electrical and Electronics Engineers (IEEE) 802.16mcommunication system.

However, if the MS is located in a sector boundary region, a soundingsignal transmitted by the MS may interfere with a sounding signaltransmitted by another MS that is in a neighbor sector, causingsignificant distortion.

Therefore, in the IEEE 802.16m communication system, a sounding resourcereuse scheme has been proposed to reduce ISI by allowing sectors to usedifferent sounding resources. However, because use of the soundingresource reuse scheme leads to a decrease in available soundingresources per sector, the number of MSs capable of transmitting asounding signal without ISI while using the same sounding subchanneldecreases in inverse proportion to the number of sectors. Thus, comparedwith an independent sounding resource distribution scheme in which allsectors use the same sounding resources, the sounding resource reusescheme disadvantageously suffers from a decrease in Multi User Diversity(MUD) gain by opportunistic scheduling.

To overcome the shortcomings of the sounding resource reuse scheme, amulti-symbol sounding resource reuse scheme has been proposed in theIEEE 802.16m communication system. The multi-symbol sounding resourcereuse scheme allows a plurality of MSs to simultaneously transmitsounding signals, by using not only Frequency Division Multiplexing(FDM) and Code Division Multiplexing (CDM) but also Time DivisionMultiplexing (TDM). Therefore, in the multi-symbol sounding resourcereuse scheme, the same number of MSs as that in the independent soundingresource distribution scheme can transmit sounding signals without ISI.

However, the multi-symbol sounding resource reuse scheme increases inratio of sounding resources to the total available uplink resources andthus decreases in uplink resources for data transmission, causing areduction in data transmission efficiency.

In addition, disadvantageously, both the multi-symbol sounding resourcereuse scheme and the independent sounding resource distribution schemeare inefficiently high in terms of sounding signal transmission overheadof each MS because neither scheme of allocating sounding resourcesconsiders channel information of MSs.

Therefore, there is a need for a sounding signal transmission/receptionmethod capable of minimizing ISI while minimizing the sounding resourcesused.

SUMMARY OF THE INVENTION

To address the above-discussed deficiencies of the prior art, it is aprimary object to provide at least the advantages described below.Accordingly, an aspect of the embodiments of the present invention is toprovide an apparatus and method for transmitting and receiving asounding signal in a wireless communication system.

Another aspect of the embodiments of the present invention is to providean apparatus and method for transmitting and receiving a sounding signalusing channel information of an MS in a wireless communication system.

In accordance with one aspect of the present invention, there isprovided a sounding signal receiving apparatus in a wirelesscommunication system. The apparatus includes a transmitter fortransmitting at least one sounding subchannel determining parameter to asounding signal transmitting apparatus. A controller determines asounding subchannel for the sounding signal transmitting apparatusaccording to the sounding subchannel determining parameter. A soundingsubchannel allocator allocates a sounding subchannel for the soundingsignal transmitting apparatus under control of the controller. And areceiver receives a sounding signal from the sounding signaltransmitting apparatus over the allocated sounding subchannel. Thesounding subchannel determining parameter may be determined forallocating a sounding subchannel considering a frequency correlation.

In accordance with another aspect of the present invention, there isprovided a sounding signal transmitting apparatus in a wirelesscommunication system. The apparatus includes a receiver for receiving atleast one sounding subchannel determining parameter from a soundingsignal receiving apparatus. A controller determines a soundingsubchannel according to the sounding subchannel determining parameter. Asounding subchannel allocator allocates the sounding subchannel undercontrol of the controller. And a transmitter for transmits a soundingsignal to the sounding signal receiving apparatus over the allocatedsounding subchannel. The sounding subchannel determining parameter maybe determined for allocating a sounding subchannel considering afrequency correlation.

In accordance with further another aspect of the present invention, amethod is provided for receiving a sounding signal by a sounding signalreceiving apparatus in a wireless communication system. The methodincludes transmitting at least one sounding subchannel determiningparameter to a sounding signal transmitting apparatus. A soundingsubchannel is allocated for the sounding signal transmitting apparatusaccording to the sounding subchannel determining parameter. And asounding signal is received from the sounding signal transmittingapparatus over the allocated sounding subchannel. The soundingsubchannel determining parameter may be determined for allocating asounding subchannel considering a frequency correlation.

In accordance with yet another aspect of the present invention, a methodis provided for transmitting a sounding signal by a sounding signaltransmitting apparatus in a wireless communication system. The methodincludes receiving at least one sounding subchannel determiningparameter from a sounding signal receiving apparatus. A soundingsubchannel is allocated according to the sounding subchannel determiningparameter. And a sounding signal is transmitted to the sounding signalreceiving apparatus over the allocated sounding subchannel. The soundingsubchannel determining parameter may be determined for allocating asounding subchannel considering a frequency correlation.

Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, itmay be advantageous to set forth definitions of certain words andphrases used throughout this patent document: the terms “include” and“comprise,” as well as derivatives thereof, mean inclusion withoutlimitation; the term “or,” is inclusive, meaning and/or; the phrases“associated with” and “associated therewith,” as well as derivativesthereof, may mean to include, be included within, interconnect with,contain, be contained within, connect to or with, couple to or with, becommunicable with, cooperate with, interleave, juxtapose, be proximateto, be bound to or with, have, have a property of, or the like; and theterm “controller” means any device, system or part thereof that controlsat least one operation, such a device may be implemented in hardware,firmware or software, or some combination of at least two of the same.It should be noted that the functionality associated with any particularcontroller may be centralized or distributed, whether locally orremotely. Definitions for certain words and phrases are providedthroughout this patent document, those of ordinary skill in the artshould understand that in many, if not most instances, such definitionsapply to prior, as well as future uses of such defined words andphrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and itsadvantages, reference is now made to the following description taken inconjunction with the accompanying drawings, in which like referencenumerals represent like parts:

The above and other aspects, features and advantages of certainembodiments of the present invention will be more apparent from thefollowing description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 schematically illustrates a configuration of a TDD OFDMcommunication system according to an embodiment of the presentinvention;

FIG. 2 illustrates a signal flow process for transmitting and receivinga sounding signal in a TDD OFDM communication system according to anembodiment of the present invention;

FIG. 3 illustrates a process for determining a sounding subchannel usingfirst-type sounding subchannel determining parameters in a TDD OFDMcommunication system according to an embodiment of the presentinvention;

FIG. 4 illustrates a process for determining a sounding subchannel usingsecond-type sounding subchannel determining parameters in a TDD OFDMcommunication system according to an embodiment of the presentinvention;

FIG. 5 illustrates a process for estimating channel information usingMMSE in a TDD OFDM communication system according to an embodiment ofthe present invention;

FIG. 6 illustrates a process for determining an MMSE filter tappermutation Φ_(k,f) in block 515 of FIG. 5;

FIG. 7 illustrates an internal structure of a BS in a TDD OFDMcommunication system according to an embodiment of the presentinvention; and

FIG. 8 illustrates an internal structure of an MS in a TDD OFDMcommunication system according to an embodiment of the presentinvention.

Throughout the drawings, the same drawing reference numerals will beunderstood to refer to the same elements, features and structures.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 through 8, discussed below, and the various embodiments used todescribe the principles of the present disclosure in this patentdocument are by way of illustration only and should not be construed inany way to limit the scope of the disclosure. Those skilled in the artwill understand that the principles of the present disclosure may beimplemented in any suitably arranged wireless communication system. Inthe following description, specific details such as detailedconfiguration and components are merely provided to assist the overallunderstanding of the embodiments of the present invention. Therefore, itshould be apparent to those skilled in the art that various changes andmodifications of the embodiments described herein can be made withoutdeparting from the scope and spirit of the invention. In addition,descriptions of well-known functions and constructions are omitted forclarity and conciseness.

The present invention provides an apparatus and method for transmittingand receiving a sounding signal in a wireless communication system.While the present invention will be described with reference to a TimeDivision Duplex (TDD) Orthogonal Frequency Division Multiplexing (OFDM)communication system as an example of the wireless communication system,the sounding signal transmission/reception apparatus and method of thepresent disclosure may also be used in other communication systems. Forconvenience of description, it is assumed herein that a Mobile Station(MS) is an example of an apparatus for transmitting a sounding signal,and a Base Station (BS) is an example of an apparatus for receiving asounding signal. Therefore, the sounding signal transmitting apparatusmay include not only the MS but also other apparatuses, and the soundingsignal receiving apparatus may also include not only the BS but alsoother apparatuses.

FIG. 1 schematically illustrates a configuration of a TDD OFDMcommunication system according to an embodiment of the presentinvention.

Referring to FIG. 1, the TDD OFDM communication system includes a BS 110and an MS 120. The BS 110 includes a plurality of sectors. For example,BS 110 includes three sectors: a sector α 111, a sector β 113, and asector γ 115, each of which uses N antennas. That is, the sector α 111uses an antenna #1 111-1 to an antenna #N 111-N, the sector β 113 usesan antenna #1 113-1 to an antenna #N 113-N, and the sector γ 115 uses anantenna #1 115-1 to an antenna #N 115-N. It is assumed that the MS 120uses one or more antennas. The MS 120 receives at least one soundingsubchannel determining parameters used to determine a soundingsubchannel and a sounding subcarrier for carrying a sounding signal,from the sector a 111 or a serving sector, and determines a soundingsubchannel and a sounding subcarrier using the received soundingsubchannel determining parameter. The sounding subchannel determiningparameter will be described in detail below.

If the MS 120 transmits a sounding signal using the determined soundingsubchannel and sounding subcarrier, the sector α 111 (or the servingsector) and the sector β 113 (or a neighbor sector) receive the soundingsignal transmitted by the MS 120.

While only one MS 120 is shown in FIG. 1, K sector boundary region MSsmay exist in coverage of the BS 110. The sector boundary region MSrepresents an MS located in a sector boundary region. While sectorstransmit signals using a multi-sector cooperative approach by way ofexample in FIG. 1, each sector may transmit a signal independently.

It addition, it is assumed that the number of subchannels used assounding subchannels in the TDD OFDM communication system is M, and eachof the M sounding subchannels includes F sounding subcarriers. In thissituation, an (N×1) sounding signal vector Y_(s)(f) that a sector s hasreceived using a sounding subcarrier f can be represented by Equation 1below, in which s represents a sector index, f represents a soundingsubcarrier index, and N represents the number of antennas used by asectors.

$\begin{matrix}{{Y_{s}(f)} = {{\sum\limits_{k = 0}^{K - 1}{{H_{s,k}(f)}{P_{k}(f)}}} + {N(f)}}} & \left\lbrack {{Eqn}.\mspace{14mu} 1} \right\rbrack\end{matrix}$

where P_(k)(f) represents a sounding signal transmitted by an MS k usinga subcarrier f, N(f) represents an (N×1) vector indicative of a Gaussiannoise component, and H_(s,k)(f) represents an (N×1) channel vector for asubcarrier f between a sector s and an MS k. Here, k represents an MSindex.

In addition, H_(s,k)(f) in Equation 1 can be expressed as Equation 2below.

$\begin{matrix}{{H_{s,k}(f)} = \begin{bmatrix}{H_{s,k}\left( {f,1} \right)} \\\vdots \\{H_{s,k}\left( {f,N} \right)}\end{bmatrix}} & \left\lbrack {{Eqn}.\mspace{14mu} 2} \right\rbrack\end{matrix}$

Where H_(s,k)(f, n) represents a channel gain between an antenna n of asector s and an MS k in a sounding subcarrier f. Here, n represents anantenna index, and H_(s,k)(f, n) in Equation 2 can be expressed asEquation 3 below.

H _(s,k)(f,n)=α_(s,k) h _(s,k)(f,n)  [Eqn. 3]

where α_(s,k)(0≦α_(s,k)≦1) represents a pass loss of a channel between asector s and an MS k, and H_(s,k)(f, n) represents an independent andidentically distributed (i.i.d.) complex Gaussian random variable withan average of ‘0’ and a variance of ‘1’.

Meanwhile, assuming that a BS including S sectors transmits a signal ina multi-sector cooperative approach using antennas of two sectors (asector s and a sector s′) neighboring a sector boundary region MS, a(2N×1) channel vector between an MS k and sectors s and s′ in a soundingsubcarrier f can be represented by Equation 4 below.

$\begin{matrix}{{H_{k}(f)} = \begin{bmatrix}{H_{s,k}(f)} \\{H_{s^{\prime},k}(f)}\end{bmatrix}} & \left\lbrack {{Eqn}.\mspace{14mu} 4} \right\rbrack\end{matrix}$

Meanwhile, the BS may estimate the channel vector H_(k)(f) using areceived sounding signal Y_(s)(E), and in this situation, a channelestimation Mean Squared Error (MSE) for an MS k is assumed to be σ_(k)². In a sector boundary region, because an MS k is located at asubstantially equal distance from the sectors s and s′, it can beassumed that α_(s,k)≈α_(s′,k)=α_(k). In this situation, a (2N+1) channelestimation vector {tilde over (H)}H_(k)(f) between an MS k and sectors sand s′ in a subcarrier f can be represented by Equation 5 below.

{tilde over (H)} _(k)(f)=H _(k)(f)+σ_(k) Z _(k)(f)  [Eqn. 5]

where Z_(k)(f) represents an (2N×1) i.i.d. complex Gaussian randomvector with an average of ‘0’ and a variance of ‘1’, and the channelvector H_(k)(f) in Equation 5 can be expressed as Equation 6 below.

$\begin{matrix}{{H_{k}(f)} = {{\frac{\alpha_{k}^{2}}{\alpha_{k}^{2} + \sigma_{k}^{2}}{{\overset{\sim}{H}}_{k}(f)}} + {\frac{\alpha_{k}\sigma_{k}}{\sqrt{\alpha_{k}^{2} + \sigma_{k}^{2}}}{Z_{k}(f)}}}} & \left\lbrack {{Eqn}.\mspace{14mu} 6} \right\rbrack\end{matrix}$

In addition, a frequency correlation R_(s,k)(Δf, n) between a channelh_(s,k)(f−Δf, n) and a channel h_(s,k)(f, n) can be represented byEquation 7 below.

R_(s,k)(Δf,n)≡E└h_(s,k)*(f−Δf,n)h_(s,k)(f,n)┘  [Eqn. 7]

where * represents a complex conjugate, and the frequency correlationR_(s,k)(Δf, n) can be regarded as R_(s,k)(Δf) because it is not affectedby antennas.

Next, a process for transmitting and receiving a sounding signal in aTDD OFDM communication system according to an embodiment of the presentinvention will be described with reference to FIG. 2.

FIG. 2 illustrates a signal flow process for transmitting and receivinga sounding signal in a TDD OFDM communication system according to anembodiment of the present invention.

Referring to FIG. 2, a BS 200 allocates sounding resources to respectivesectors in block 211. It is assumed that the BS 200 uses a soundingresource reuse scheme with a reuse factor S, where S represents thenumber of sectors included in the BS 200. When using the soundingresource reuse scheme with a reuse factor S, the BS 200 divides allavailable sounding resources into S sets, and allocates differentsounding resources to S sectors.

The BS 200 determines at least one sounding subchannel determiningparameter for an MS 210 in block 213, and transmits the determinedsounding subchannel determining parameter 215 to the MS 210. Thesounding subchannel determining parameter will be described in detailbelow.

The BS 200 determines at least one sounding subchannel and at least onesounding subcarrier to be used by the MS 210 based on the determinedsounding subchannel determining parameter in block 217. The MS 210 alsodetermines at least one sounding subchannel and at least one soundingsubcarrier using the sounding subchannel determining parameter receivedfrom the BS 200 in block 219. Because the BS 200 and the MS 210 eachdetermine the sounding subchannel and the sounding subcarrier using thesounding subchannel determining parameter, the BS 200 is not required totransmit to the MS 210 information about the sounding subchannel and thesounding subcarrier to be used by the MS 210, which reduces signalingoverhead.

The MS 210 transmits a sounding signal 221 to the BS 200 using thedetermined sounding subchannel and sounding subcarrier. The BS 200receives the sounding signal transmitted by the MS 210 using thedetermined sounding subchannel and sounding subcarrier, and estimates achannel using the received sounding signal in block 223. The channel maybe estimated using a Minimum Mean Square Error (MMSE) approach. Afterthe channel estimation, the BS 200 transmits a signal 225 using amulti-sector cooperative scheme.

The sounding subchannel determining parameter is described below.

Two types of sounding subchannel determining parameters are proposed bythe present invention. A first-type sounding subchannel determiningparameter includes an MS index k and a threshold δ_(k), and asecond-type sounding subchannel determining parameter includes an MSindex k and an overhead index O_(k).

A process for determining a sounding subchannel using a first-typesounding subchannel determining parameter in a TDD OFDM communicationsystem will be described with reference to FIG. 3.

FIG. 3 illustrates a process for determining a sounding subchannel usinga first-type sounding subchannel determining parameter in a TDD OFDMcommunication system according to an embodiment of the presentinvention.

In FIG. 3, Ω_(k) denotes a sounding subchannel set for an MS k and Θ_(k)denotes a sounding candidate subchannel set for an MS k. While thesounding subchannel and sounding subcarrier determining process will bedescribed in FIG. 3 on the assumption that a sounding subchannel and asounding subcarrier are determined by an MS for convenience ofdescription, a BS may also determine a sounding subchannel and asounding subcarrier using the sounding subchannel and soundingsubcarrier determining process described in FIG. 3.

The sounding candidate subchannel set includes sounding subchannels tobe used by an MS, and the sounding subchannel set includes soundingsubchannels selected by the MS among the sounding subchannels in thesounding candidate subchannel set.

Referring to FIG. 3, an MS initiates a variable i and a soundingsubchannel set Ω_(k) in block 311. The variable i and the soundingsubchannel set Ω_(k) are initiated as i=1 and Θ_(k)=Ø, respectively. Inblock 313, the MS determines a sounding candidate subchannel set inaccordance with Equation 8 below.

Θ_(k)(j)=└j(4k ²+1)+k,mod,M┘ for 0≦j≦M−1  [Eqn. 8]

where Θ_(k)(j) represents a j-th element among elements in a soundingcandidate subchannel set Θ_(k), and [k, mod, M] represents a remainderof an operation of dividing ‘k’ by ‘M’.

In block 315, the MS updates the sounding subchannel set Ω_(k) and thesounding candidate subchannel set Θ_(k) using a frequency correlation inaccordance with Equation 9 below.

{circumflex over (m)} _(k,i)=Θ_(k)(0)

Ω_(k)←Ω_(k)∪{{circumflex over (m)}_(k,i)}

Θ_(k) ={mεΘ _(k) ∥R _(s,k)((m−{circumflex over (m)}_(k,i))F)|<δ_(k)}  [Eqn. 9]

where δ_(k) represents a frequency correlation threshold for an MS k, mdenotes an element of a candidate subchannel set Θ_(k), and {circumflexover (m)}_(k,i) denotes a sounding subchannel set.

In block 317, the MS determines whether Θ_(k)=0, i.e., whether there areno elements in the sounding candidate subchannel set Θ_(k). If Θ_(k)=Ø,the MS increases a value of the variable i by a preset value, e.g., 1(i←i+1) and then returns to block 315.

However, if Θ_(k)≠Ø, the MS decides (or settles) the sounding subchannelset Ω_(k) in block 319 in accordance with Equation 10.

$\begin{matrix}{\Omega_{k} = \begin{bmatrix}{\hat{m}}_{k,1} \\\vdots \\{\hat{m}}_{k,i}\end{bmatrix}} & \left\lbrack {{Eqn}.\mspace{14mu} 10} \right\rbrack\end{matrix}$

By determining sounding subchannels using the first-type soundingsubchannel determining parameter as described in FIG. 3, the followinggain may be acquired.

First, because sounding signals are transmitted and received using onlythe sounding subchannels whose frequency correlation is lower than athreshold δ_(k) as represented in Equation 9, the proposed scheme mayreduce signaling overhead required for sounding signaltransmission/reception, compared with the conventional sounding signaltransmission/reception scheme using the entire frequency band.

In addition, because the sounding subchannel set Ω_(k), decided as shownin Equation 10, is determined using an MS index, a threshold, and afrequency correlation that are shared by a BS and an MS, the BS is notrequired to transmit information related to allocation of soundingsubchannels to the MS separately.

Also, a different sounding candidate subchannel set Θ_(k) is created forevery MS, thereby reducing the probability that MSs will transmitsounding signals using the same sounding subchannels, and thusminimizing interference between a sounding signal transmitted by aspecific MS and a sounding signal transmitted by another MS.

Next, a process for determining a sounding subchannel using asecond-type sounding subchannel determining parameter in a TDD OFDMcommunication system will be described with reference to FIG. 4.

FIG. 4 illustrates a process for determining a sounding subchannel usinga second-type sounding subchannel determining parameter in a TDD OFDMcommunication system according to an embodiment of the presentinvention.

While the sounding subchannel and sounding subcarrier determining methodwill be described in FIG. 4 on the assumption that a sounding subchanneland a sounding subcarrier are determined by an MS for convenience ofdescription, a BS may also determine a sounding subchannel and asounding subcarrier using the sounding subchannel and soundingsubcarrier determining method described in FIG. 4.

Referring to FIG. 4, an MS initiates a variable i and a soundingsubchannel set Ω_(k) in accordance with Equation 11 in block 411.

i=1,{circumflex over (m)} _(k,1)=└4k ² +k+1,mod,M┘,Ω _(k)≡{{circumflexover (m)}_(k,1)}  [Eqn. 11]

In block 413, the MS determines whether |Ω_(k)|<O_(k). If |Ω_(k)|O_(k),the MS increases a value of the variable i by a preset value, e.g., 1(i←i+1) and then proceeds to block 415. In block 415, the MS updates thesounding subchannel set Ω_(k) in accordance with Equation 12 below usinga frequency correlation.

$\begin{matrix}{{{\hat{m}}_{k,i} = {\min\limits_{m_{k}^{\prime} \notin \Omega_{k}}\left( {\max\limits_{{\hat{m}}_{k} \in \Omega_{k}}{{R_{s,k}\left( {\left( {m_{k}^{\prime} - {\hat{m}}_{k}} \right)F} \right)}}} \right)}},\left. \Omega_{k}\leftarrow{\Omega_{k}\bigcup\left\{ {\hat{m}}_{k,i} \right\}} \right.} & \left\lbrack {{Eqn}.\mspace{14mu} 12} \right\rbrack\end{matrix}$

where, m′_(k) denotes an element of

However, if |Ω_(k)|=O_(k) in block 413, the MS decides the soundingsubchannel set Ω_(k) in accordance with Equation 13 in block 417.

$\begin{matrix}{\Omega_{k} = \begin{bmatrix}{\hat{m}}_{k,1} \\\vdots \\{\hat{m}}_{k,O_{k}}\end{bmatrix}} & \left\lbrack {{Eqn}.\mspace{14mu} 13} \right\rbrack\end{matrix}$

By determining sounding subchannels using the second-type soundingsubchannel determining parameter as described in FIG. 4, the followinggains may be obtained.

First, because sounding signals are transmitted and received using onlyO_(k) sounding subchannels with a low frequency correlation asrepresented in Equation 12, the proposed scheme may reduce signalingoverhead required for sounding signal transmission/reception, comparedwith the conventional sounding signal transmission/reception schemeusing the entire frequency band.

In addition, because the sounding subchannel set Ω_(k), decided as shownin Equation 13, is determined using an MS index, an overhead index, anda frequency correlation that are shared by a BS and an MS, the BS is notrequired to transmit information associated with allocation of soundingsubchannels to the MS separately.

Also, a different initial sounding subchannel set {circumflex over(m)}_(k,1) is created for every MS as described in block 411, therebyreducing the probability that MSs will transmit sounding signals usingthe same sounding subchannels, and thus minimizing interference betweena sounding signal transmitted by a specific MS and a sounding signaltransmitted by another MS.

After determining sounding subchannels using the first-type soundingsubchannel determining parameter and the second-type sounding subchanneldetermining parameter (i.e., after deciding the sounding subchannel setΩ_(k) using the first-type sounding subchannel determining parameter andthe second-type sounding subchannel determining parameter) the MSdetermines a sounding subcarrier used to actually transmit a soundingsignal among sounding subcarriers included in its sounding subchannel inaccordance with Equation 14 below.

$\begin{matrix}{\Lambda_{s,k} = \left\{ {\left. {{{\hat{m}}_{k}F} + \frac{Fs}{S} + \left\lbrack {{k + {Dd}},{mod},\frac{F}{S}} \right\rbrack} \middle| {{\hat{m}}_{k} \in \Omega_{k}} \right.,{0 \leq d \leq {\left\lfloor \frac{F}{SD} \right\rfloor - 1}},{{{and}\mspace{14mu} 1} \leq D \leq \frac{F}{S}}} \right\}} & \left\lbrack {{Eqn}.\mspace{14mu} 14} \right\rbrack\end{matrix}$

where D represents a decimation index, and each MS may increase soundingsignal's transmit power up to DS times an average transmit power P_(o).

Next, a process for estimating channel information using MMSE in a TDDOFDM communication system according to an embodiment of the presentinvention will be described with reference to FIG. 5.

FIG. 5 illustrates a process for estimating channel information usingMMSE in a TDD OFDM communication system according to an embodiment ofthe present invention.

Referring to FIG. 5, a BS receives a sounding signal from an MS in block511. In block 513, the BS estimates a channel vector of a soundingsubcarrier {circumflex over (f)}(δΛ_(s,k)) using a channel estimationscheme such as Least Square (LS), in accordance with Equation 15.

$\begin{matrix}{{{{\overset{\sim}{H}}_{s,k}\left( {\hat{f}}_{k} \right)} = {\frac{1}{{DSP}_{0}}{Y_{s}\left( {\hat{f}}_{k} \right)}}},{{{for}\mspace{14mu} {\hat{f}}_{k}} \in \Lambda_{s,k}}} & \left\lbrack {{Eqn}.\mspace{14mu} 15} \right\rbrack\end{matrix}$

In block 515, the BS determines an MMSE filter tap permutation Φ_(k,f)including T_(k) subcarriers to estimate a channel vector H_(s,k)(f) of asubcarrier f(0≦f≦MF−1) for an MS k with a low MSE, and then proceeds toblock 517.

A process for determining the MMSE filter tap permutation Φ_(k,f) willbe described with reference to FIG. 6.

FIG. 6 illustrates a process for determining the MMSE filter tappermutation Φ_(k f) in block 515 of FIG. 5.

Referring to FIG. 6, the BS initiates a variable i and an MMSE filtertap permutation Φ_(k,f) in block 611 (i=1 and Φ_(k,f)=Ø). In block 613,the BS updates the MMSE filter tap permutation Φ_(k,f) using a frequencycorrelation in accordance with Equation 16 below.

$\begin{matrix}{{\Phi_{k,f}(i)} = {\underset{{\hat{f}}_{k} \in {\Lambda_{s,k} - \Phi_{k,f}}}{\arg \mspace{14mu} \max}{{R_{s,k}\left( {f - {\hat{f}}_{k}} \right)}}}} & \left\lbrack {{Eqn}.\mspace{14mu} 16} \right\rbrack\end{matrix}$

where Θ_(k,f)(i) represents an i-th element in an MMSE filter tappermutation Φ_(k,f).

In block 615, the BS determines whether |Φ_(k,f)|T_(k). If so, the BSreturns to block 613 after increasing a value of the variable i by apreset value, e.g., 1 (i←i+1).

However, if |Φ_(k,f)|≧T_(k) in block 615, the BS decides the MMSE filtertap permutation Φ_(k,f) in accordance with Equation 17 below in block617.

$\begin{matrix}{\Phi_{k,f} = \begin{bmatrix}{\Phi_{k,f}(1)} \\\vdots \\{\Phi_{k,f}\left( T_{k} \right)}\end{bmatrix}} & \left\lbrack {{Eqn}.\mspace{14mu} 17} \right\rbrack\end{matrix}$

Referring back to FIG. 5, in block 517, the BS determines a channelestimation vector {tilde over (H)}_(s,k)(f) of a subcarrier f inaccordance with Equation 18 using an MMSE channel estimation scheme thatuses an MMSE filter tap permutation Φ_(k,f) and a frequency correlation.

{tilde over (H)} _(s,k)(f)=(C _(s,k)(f,Φ _(k,f))R _(s,k)⁻¹(Φ_(k,f)){tilde over (H)} _(s,k) ^(T)(Φ_(k,f))^(T)  [Eqn. 18]

where T represents a transpose matrix operation, and C_(s,k)(f, Φ_(k,f))represents a cross correlation vector between a subcarrier f and afilter tap permutation Φ_(k,f), and can be expressed as Equation 19)below.

C _(s,k)(Φ_(k,f))=[R _(s,k)(f−Φ _(k,f)(1)R _(s,k)(f−Φ _(k,f)(2)) . . . R_(s,k)(f−Φ _(k,f)(T _(k)))]  [Eqn. 19]

Furthermore, R_(s,k)(Φ_(k,f)) in Equation 18 represents an autocorrelation matrix of a filter tap permutation Φ_(k,f), and can beexpressed as Equation 20 below.

$\begin{matrix}{{R_{s,k}\left( \Phi_{k,f} \right)} = \left\lbrack \begin{matrix}{R_{s,k}\left( {{\Phi_{k,f}(1)} - {\Phi_{k,f}(1)}} \right)} & \ldots & {R_{s,k}\left( {{\Phi_{k,f}(1)} - {\Phi_{k,f}\left( T_{k} \right)}} \right)} \\\vdots & \ddots & \vdots \\{R_{s,k}\left( {{\Phi_{k,f}\left( T_{k} \right)} - {\Phi_{k,f}(1)}} \right)} & \ldots & {R_{s,k}\left( {{\Phi_{k,f}\left( T_{k} \right)} - {\Phi_{k,f}\left( T_{k} \right)}} \right)}\end{matrix} \right\rbrack} & \left\lbrack {{Eqn}.\mspace{14mu} 20} \right\rbrack\end{matrix}$

In addition, {tilde over (H)}_(s,k)(Φ_(k,f)) in Equation 18 represents achannel estimation matrix for an MMSE filter tap permutation Φ_(k,f) andcan be expressed as Equation 21 below.

{tilde over (H)} _(s,k)(Φ_(k,f))=[{tilde over (H)}_(s,k)(Φ_(k,f)(1)){tilde over (H)} _(s,k)(Φ_(k,f)(2)) . . . {tilde over(H)} _(s,k)(Φ_(k,f)(T _(k)))]  [Eqn. 21]

Meanwhile, the BS can perform multi-sector cooperative transmissionusing sounding channel information. A process in which a BS performsmulti-sector cooperative transmission using sounding channel informationis described below.

First, the BS estimates a Signal-to-Interference plus Noise Ratio (SINR){tilde over (γ)}_(k)(f) for a subcarrier f used by an MS k in accordancewith Equation 22 below using a channel estimation vector {tilde over(H)}_(k)(f).

{tilde over (γ)}_(k)(f)=γ₀∥{tilde over (H)}_(k)(f)∥²  [Eqn. 22]

where γ_(O) represents an average SINR, and ∥E∥ represents a vector normfunction of E.

The BS selects an MS π_(f)(=arg max_(k={0, . . . , K-1}){{tilde over(γ)}_(k)(f)}) with the highest SINR in a subcarrier f, generates a beamw_(π) _(f) (f) in accordance with Equation 23, and cooperativelytransmits a signal using the generated beam.

$\begin{matrix}{{w_{\pi_{f}}(f)} = \frac{{\overset{\sim}{H}}_{\pi_{f}}^{*}(f)}{{{\overset{\sim}{H}}_{\pi_{f}}(f)}}} & \left\lbrack {{Eqn}.\mspace{14mu} 23} \right\rbrack\end{matrix}$

When a BS performs multi-sector cooperative transmission as describedabove, its performance may be analyzed as follows.

First, a received signal r_(π) _(f) (f) of an MS π_(f) for a cooperativebeam W_(π) _(f) (f) in Equation 23 can be represented by Equation 24below.

r _(π) _(f) (f)=H _(π) _(T) (f)w _(π) _(f) (f)X _(π) _(f)(f)+N(f)  [Eqn. 24]

where X_(π) _(f) (f) represents a data signal for a subcarrier f used byan MS π_(f), and N(f) represents a Gaussian noise.

In addition, a received SINR γ_(π) _(f) (f) for the received signalr_(π) _(f) (f) can be defined as Equation 25 below.

$\begin{matrix}\begin{matrix}{{\gamma_{\pi_{f}}(f)} = {2\gamma_{0}{{{H_{\pi_{f}}^{T}(f)}{w_{\pi_{f}}(f)}}}^{2}}} \\{= {2\gamma_{0}\frac{{\begin{matrix}{{\frac{\alpha_{\pi_{f}}^{2}}{\alpha_{\pi_{f}}^{2} + \sigma_{\pi_{f}}^{2}}{{{\overset{\sim}{H}}_{\pi_{f}}(f)}}^{2}} +} \\{\frac{\alpha_{\pi_{f}}\sigma_{\pi_{f}}}{\sqrt{\alpha_{\pi_{f}}^{2} + \sigma_{\pi_{f}}^{2}}}{Z_{\pi_{f}}^{T}(f)}{{\overset{\sim}{H}}_{\pi_{f}}^{*}(f)}}\end{matrix}}^{2}}{{{{\overset{\sim}{H}}_{\pi_{f}}(f)}}^{2}}}}\end{matrix} & \left\lbrack {{Eqn}.\mspace{14mu} 25} \right\rbrack\end{matrix}$

For α_(π) _(f) =α and α_(π) _(f) ²α², an expected value γ of thereceived SINR can be calculated using Equation 26 below.

$\begin{matrix}\begin{matrix}{\overset{\_}{\gamma} = {E\left\lfloor {\gamma_{\pi_{f}}(f)} \right\rfloor}} \\{= {\frac{2\alpha^{2}\gamma_{0}}{\alpha^{2} + \sigma^{2}}\left( {{\frac{\alpha^{2}}{\alpha^{2} + \sigma^{2}}{E\left\lbrack {{{\overset{\sim}{H}}_{\pi_{f}}(f)}}^{2} \right\rbrack}} + \sigma^{2}} \right)}} \\{\leq {\frac{2\alpha^{2}\gamma_{0}}{\alpha^{2} + \sigma^{2}}\left( {{2\alpha^{2}N{\sum\limits_{k = 1}^{K}\frac{1}{K}}} + \sigma^{2}} \right)}}\end{matrix} & \left\lbrack {{Eqn}.\mspace{14mu} 26} \right\rbrack\end{matrix}$

The expected value γ of the received SINR increases with an increase inthe number K of MSs or a decrease in a sounding channel estimation MSEσ².

By transmitting and receiving sounding signals as proposed by thepresent disclosure, full-band channel information may be provided to aplurality of MSs with a low MSE, making it possible to maximizemulti-sector cooperative transmission performance.

An internal structure of a BS in a TDD OFDM communication systemaccording to an embodiment of the present invention will now bedescribed with reference to FIG. 7.

FIG. 7 illustrates an internal structure of a BS in a TDD OFDMcommunication system according to an embodiment of the presentinvention.

Referring to FIG. 7, the BS includes a transmitter 711, a controller713, a sounding channel allocator 715, and a receiver 717.

The controller 713 controls the overall operation of the BS anddetermines a sounding subchannel and a sounding subcarrier for aspecific MS using a first-type sounding subchannel determining parameteror a second-type sounding subchannel determining parameter. Thecontroller 713 controls the sounding channel allocator 715 to allocate asounding channel so as to correspond to the determined soundingsubchannel and sounding subcarrier. The sounding channel allocator 715allocates a sounding channel for the MS under control of the controller713.

The transmitter 711 transmits the first-type sounding subchanneldetermining parameter or the second-type sounding subchannel determiningparameter to the MS under control of the controller 713. The receiver717 receives a sounding signal from the MS using a sounding channelallocated by the sounding channel allocator 715. The controller 713estimates a channel using the sounding signal. The operation of thecontroller 713 has been described in FIGS. 2 to 6.

Next, an internal structure of an MS in a TDD OFDM communication systemaccording to an embodiment of the present invention will be describedwith reference to FIG. 8.

FIG. 8 illustrates an internal structure of an MS in a TDD OFDMcommunication system according to an embodiment of the presentinvention.

Referring to FIG. 8, the MS includes a receiver 811, a controller 813, asounding channel allocator 815, and a transmitter 817.

The controller 813 controls the overall operation of the MS, anddetermines a sounding subchannel and a sounding subcarrier to be used byits MS using a first-type sounding subchannel determining parameter or asecond-type sounding subchannel determining parameter. The controller813 controls the sounding channel allocator 815 to allocate a soundingchannel so as to correspond to the determined sounding subchannel andsounding subcarrier. The sounding channel allocator 815 allocates asounding channel to be used by its MS under control of the controller813.

The receiver 811 receives the first-type sounding subchannel determiningparameter or the second-type sounding subchannel determining parameterfrom the BS. The transmitter 817 transmits a sounding signal to the BSusing the sounding channel allocated by the sounding channel allocator815. The operation of the controller 813 has been described in FIGS. 2and 3.

As is apparent from the foregoing description, according to anembodiment of the present invention, sounding signals can be transmittedand received using channel information of MSs in a wirelesscommunication system, thereby minimizing ISI while minimizing soundingresources used for transmission/reception of sounding signals. Inaddition, sounding subchannels and sounding subcarriers may bedetermined by an MS and a BS independently in a wireless communicationsystem, thereby reducing signaling overhead required fortransmission/reception of sounding subchannels and sounding subcarriers.

Although the present disclosure has been described with an exemplaryembodiment, various changes and modifications may be suggested to oneskilled in the art. It is intended that the present disclosure encompasssuch changes and modifications as fall within the scope of the appendedclaims.

1. A method for receiving a sounding signal by a sounding signalreceiving apparatus in a wireless communication system, the methodcomprising: transmitting at least one sounding subchannel determiningparameter to a sounding signal transmitting apparatus; allocating asounding subchannel for the sounding signal transmitting apparatusaccording to the sounding subchannel determining parameter; andreceiving a sounding signal from the sounding signal transmittingapparatus over the allocated sounding subchannel, wherein the soundingsubchannel determining parameter is determined for allocating a soundingsubchannel based on a frequency correlation.
 2. The method of claim 1,wherein the sounding subchannel determining parameter includes asounding signal transmitting apparatus index and a threshold.
 3. Themethod of claim 1, wherein allocating the sounding subchannel comprisesallocating a sounding subchannel for the sounding signal transmittingapparatus using a sounding subchannel set including sounding subchannelsto be used by the sounding signal transmitting apparatus and a soundingcandidate subchannel set including sounding subchannels selected by thesounding signal transmitting apparatus among sounding subchannelsincluded in the sounding subchannel set.
 4. The method of claim 1,wherein the sounding subchannel determining parameter includes asounding signal transmitting apparatus index and an overhead index. 5.The method of claim 1, further comprising: estimating a channel based onthe sounding signal received from the sounding signal transmittingapparatus; and transmitting a multi-sector cooperative scheme to thesounding signal transmitting apparatus.
 6. A method for transmitting asounding signal by a sounding signal transmitting apparatus in awireless communication system, the method comprising: receiving at leastone sounding subchannel determining parameter from a sounding signalreceiving apparatus; allocating a sounding subchannel according to thesounding subchannel determining parameter; and transmitting a soundingsignal to the sounding signal receiving apparatus over the allocatedsounding subchannel, wherein the sounding subchannel determiningparameter is determined for allocating a sounding subchannel based on afrequency correlation.
 7. The method of claim 6, wherein the soundingsubchannel determining parameter includes a sounding signal transmittingapparatus index and a threshold.
 8. The method of claim 6, whereinallocating the sounding subchannel comprises allocating a soundingsubchannel for the sounding signal transmitting apparatus using asounding subchannel set including sounding subchannels to be used by thesounding signal transmitting apparatus and a sounding candidatesubchannel set including sounding subchannels selected by the soundingsignal transmitting apparatus among sounding subchannels included in thesounding subchannel set.
 9. The method of claim 6, wherein the soundingsubchannel determining parameter includes a sounding signal transmittingapparatus index and an overhead index.
 10. The method of claim 6,wherein transmitting the sounding signal comprises selecting asubcarrier from among a set of subcarriers associated with the allocatedsounding subchannel.
 11. A sounding signal receiving apparatus in awireless communication system, the sounding signal receiving apparatuscomprising: a transmitter configured to transmit at least one soundingsubchannel determining parameter to a sounding signal transmittingapparatus; a controller configured to determine a sounding subchannelfor the sounding signal transmitting apparatus according to the soundingsubchannel determining parameter; a sounding subchannel allocatorconfigured to allocate a sounding subchannel for the sounding signaltransmitting apparatus under control of the controller; and a receiverconfigured to receive a sounding signal from the sounding signaltransmitting apparatus over the allocated sounding subchannel, whereinthe sounding subchannel determining parameter is determined forallocating a sounding subchannel based on a frequency correlation. 12.The sounding signal receiving apparatus of claim 11, wherein thesounding subchannel determining parameter includes a sounding signaltransmitting apparatus index and a threshold.
 13. The sounding signalreceiving apparatus of claim 11, wherein the controller determines asounding subchannel for the sounding signal transmitting apparatus usinga sounding subchannel set including sounding subchannels to be used bythe sounding signal transmitting apparatus, and a sounding candidatesubchannel set including sounding subchannels selected by the soundingsignal transmitting apparatus among sounding subchannels included in thesounding subchannel set.
 14. The sounding signal receiving apparatus ofclaim 11, wherein the sounding subchannel determining parameter includesa sounding signal transmitting apparatus index and an overhead index.15. The sounding signal receiving apparatus of claim 11, wherein thecontroller is further configured to estimate a channel based on thesounding signal received from the sounding signal transmitting apparatusand transmit a multi-sector cooperative scheme to the sounding signaltransmitting apparatus.
 16. A sounding signal transmitting apparatus ina wireless communication system, the sounding signal transmittingapparatus comprising: a receiver configured to receive at least onesounding subchannel determining parameter from a sounding signalreceiving apparatus; a controller configured to determine a soundingsubchannel according to the sounding subchannel determining parameter; asounding subchannel allocator configured to allocate the soundingsubchannel under control of the controller; and a transmitter configuredto transmit a sounding signal to the sounding signal receiving apparatusover the allocated sounding subchannel; wherein the sounding subchanneldetermining parameter is determined for allocating a sounding subchannelconsidering a frequency correlation.
 17. The sounding signaltransmitting apparatus of claim 16, wherein the sounding subchanneldetermining parameter includes a sounding signal transmitting apparatusindex and a threshold.
 18. The sounding signal transmitting apparatus ofclaim 16, wherein the controller determines a sounding subchannel forthe sounding signal transmitting apparatus using a sounding subchannelset including sounding subchannels to be used by the sounding signaltransmitting apparatus, and a sounding candidate subchannel setincluding sounding subchannels selected by the sounding signaltransmitting apparatus among sounding subchannels included in thesounding subchannel set.
 19. The sounding signal transmitting apparatusof claim 16, wherein the sounding subchannel determining parameterincludes a sounding signal transmitting apparatus index and an overheadindex.
 20. The sounding signal transmitting apparatus of claim 16,wherein the controller is further configured to select a subcarrier fromamong a set of subcarriers associated with the allocated soundingsubchannel.